The only risks for HIV in adults are:
1) Having unprotected anal or vaginal sex, or
2) sharing intravenous needles with IV drug users.
You aren't really putting yourself at risk for HIV here, although having multiple partners means that you should occasionally test for HIV and STDs, just to ensure that you're disease-free. I certainly wouldn't worry about it, but if you're concerned, insist that your partners wear condoms when you give them oral.